Conventionally, a lamp light source has been mainly used as a light source of a projection-type image display apparatus. However, the lamp light source has a disadvantage of short lifetime. Therefore, a surface-emission light source such as a light emitting diode (LED) having a longer lifetime is recently used in replacement of the lamp light source. Light emitted from a monochromatic color LED has a narrow wavelength band. Therefore, a wide color reproduction area can be obtained by using LEDs of red (R), green (G) and blue (B) in combination.
In order to enhance light use efficiency, Patent Document 1 discloses an illumination optical system using LEDs of R, G and B having rectangular light emitting surfaces. Light emitted from arbitrary points on the respective light emitting surfaces is parallelized by collimator optical systems, and combined by a dichroic mirror. The combined light is converged by a converging lens on an incident surface of an integrator rod. The illumination optical system forms a light source image of the LED (i.e., an image of the light emitting surface) on the incident surface of the integrator rod at a predetermined magnification.
Further, in an application of an odd-shaped display such as an extremely horizontally oblong display, there are cases where an aspect ratio of the light emitting surface and an aspect ratio of a screen shape of the display are different from each other. In such a case, the light source illuminates an area of the image display element whose aspect ratio is different from that of the light emitting surface, and therefore loss of light quantity occurs.
Then, Patent Document 2 proposes a configuration in which a toric lens is provided in a light path of the illumination optical system of the projection type image display apparatus so as to change the aspect ratio of the light emitting surface of the light source.